The term “packaging” applied to diode-laser bars refers to mounting a diode-laser bar, or an array of diode-laser bars, on some sort of cooling-base or heat-sink. This base may be a relatively massive base providing a “conductively cooled package” (CCP). For higher power operation, the base is typically water-cooled, for example by a micro-channel arrangement.
A diode-laser bar includes a plurality of semiconductor layers epitaxially grown on a single-crystal substrate, with a plurality of diode-laser emitters defined in the epitaxial layers. Typically, the substrate is an n-type substrate, and layers are grown such that layers forming the “p-side” (anode-side) of the diodes are uppermost. The diode-laser bar is soldered “p-side down” either directly onto the heat-sink or via a sub-mount having a coefficient of thermal expansion (CTE) intermediate that of the substrate material and the heat-sink material, which is usually copper.
Electrical connection to the diode-laser bars places the heat-sink and cooling-water therein, in electrical contact with the diode-laser bar energizing circuit. In an array of diode-laser bars, the water can short-circuit electric connection to the bars unless the electrical conductivity of the water is low. A common solution to this is to use de-ionized (DI) or high-resistance water. However, DI water is more corrosive on metals than water from conventional building supplies, and the use of de-ionized water is expensive and inconvenient by comparison. There is a need for an improved water-cooled package for diode-laser bars that does not require the use of de-ionized water for the water-cooling.